In a known inkjet print head, a droplet forming unit is be manufactured by lithographic techniques in a layered silicon plate, thus forming a MEMS chip. Such a MEMS chip based inkjet print head is difficult to handle and ink needs to be supplied to the MEMS chip. Thereto, it is known to arrange the MEMS chip on an ink supply substrate which provides for a fluidic coupling to an ink reservoir and which enables handling and positioning of the inkjet print head in an inkjet printer assembly.
The ink supply substrate is commonly not made of silicon, which results in the MEMS chip and the ink supply substrate having different respective coefficients of thermal expansion. As a consequence, when operating the inkjet print head at a temperature different than the temperature at which the MEMS chip was adhered to the ink supply substrate, the MEMS chip will have expanded or contracted with an amount different than the ink supply substrate. The different amount of expansion or contraction affects the shape of the ink supply substrate and/or the MEMS chip. Since it may be expected that the ink supply substrate is stiffer than the MEMS chip, the MEMS chip will deform significantly, while any deformation in the ink supply substrate will be limited.
Any deformation in the MEMS droplet forming unit will affect the droplet forming. For example, a direction of droplet ejection may be deviated. In another example, the MEMS droplet forming unit may be a piezo-actuated droplet forming unit using a piezo actuator arranged on a membrane. Deformation of the MEMS chip will then result in a change in stress in the membrane, but not equally for all membranes, resulting in different droplet ejection properties, such as different droplet speed and/or different droplet size and/or different droplet directions.